Another thought comes to mind on this.
There's a spec called XPointer. This
is based on XPath, but extends its semantics in various ways.
Quick skim of this suggests to me that
we would not be entirely out of line to make the extensions we need. E.g.,
consider this section excerpted from the XPointer 1.0 document:
5 XPointer Extensions to XPath
XPointer extends XPath by adding the following:
- A generalization of the XPath concepts of nodes, node
types, and node-sets to the XPointer concepts of locations,
location types, and location-sets, which subsume
nodes, points,
and ranges.
- Two new location types, point
and range, corresponding
to DOM positions and ranges, that can appear in location-set results; also
tests (akin to node tests) for these location types.
- Rules for establishing the XPath evaluation context.
- The functions string-range
and range-to, which return
the range location type for selections that are not single XML nodes.
- The functions here
and origin, to provide
for addressing relative to the location of an XPointer expression itself,
and to the point of origin for hypertext traversal when XPointers are used
in that (very common) application domain.
- The functions start-point
and end-point, to address
the beginning and ending locations which bound another location such as
a node or range.
- Like [XSLT],
XPointer allows the root node to have multiple child elements, to allow
XPointers to address into arbitrary external parsed entities as well as
well-formed documents.
I find the last bullet particularly
interesting as the XSD/XML insistance on a single top document node for
all data is generally annoying and simply artificial for much non-XML data.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Robert E. McGrath"
<mcgrath@ncsa.uiuc.edu>
Sent by: owner-dfdl-wg@ggf.org
01/19/2006 10:00 AM
|
|
To
| dfdl-wg@ggf.org
|
|
cc
|
|
|
Subject
| Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements |
|
I would want to change XPath only as a last resort.
(Any of the
options is OK by me, assuming we have to mess with the Xpath
at all.)
Can we deal with this some other way?
Can we document the problematic cases, and suggest best practices that
will minimize the problem?
On Thursday 19 January 2006 08:45, Suman Kalia wrote:
> I fully agree with Steve - let's not invent another XPATH like syntax
..
>
> Suman Kalia
> IBM Toronto Lab
> WebSphere Business Integration Application Connectivity Tools
> Tel : 905-413-3923 T/L 969-3923
> Fax : 905-413-4850
> Internet ID : kalia@ca.ibm.com
> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>
> Steve Hanson <smh@uk.ibm.com>
> Sent by: owner-dfdl-wg@ggf.org
> 01/19/2006 04:43 AM
>
> To
> "Westhead, Martin (Martin)" <westhead@avaya.com>
> cc
> dfdl-wg@ggf.org, owner-dfdl-wg@ggf.org
> Subject
> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>
>
>
>
> As a DFDL parser implementor I do not want modifications to the XPath
> syntax. I want to be able to reuse existing XPath implementations.
It's
> also something else for the user to have to learn. So 2a/b/c are not
> attractive.
>
> Regards, Steve
>
> Steve Hanson
> WebSphere Message Brokers,
> IBM Hursley, England
> Internet: smh@uk.ibm.com
> Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> (Martin)"
> <westhead@avaya.c
To
>
> om>
<dfdl-wg@ggf.org>
> Sent by:
cc
>
> owner-dfdl-wg@ggf
> .org
Subject
>
>
[dfdl-wg]
Ambiguous XPaths to
>
hidden
elements
> 18/01/2006 20:24
>
>
>
>
>
>
>
>
>
> Hi folks,
>
> This is to try to pick up on the issue identified by Suman in today?s
> call.
>
> The Issue
> Consider the following example:
>
> <xs:element name="root">
> <xs:complexType>
>
<xs:sequence>
>
<xs:annotation><xs:appinfo
> source=?http://dataformat.org? />
>
<hidden>
> <xs:element name="repeats" type="xs:integer"/>
>
</hidden>
>
> </xs:appinfo></xs:annotation >
>
<xs:element name="testElement"
> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
>
dfdl:repeatCount=?../repeats?>
> </xs:complexType>
> </xs:element>
>
> The problem is that the path ?../repeats? can be broken by modifications
> to
> the logical model due to name clashes on ?repeats? and there are cases
> that
> can be constructed where this would not be obvious to a user.
>
> Possible Solutions
> Possible fixes to this include:
> 1. Disallow XPath references to hidden
elements the user is forced
> to
> place the material into the global context to
refer to it.
> 2. Provide a special XPath operator
to indicate we are referencing
> a
> hidden element, possibilities include:
> a. ?../hidden(repeats)?
> b. ?hidden(../repeats)?
> c. ?../dfdl:hidden/repeats?
> 3. Only allow hidden elements to be present in
top level global
> complex
> types. These can then be included where needed.
(This is the
> solution
> that Suman was pushing but
I don?t fully understand it ?
> in
> particular I don?t see how it resolves the ambiguity
issue.)
>
>
> I believe my preference here is 2a or 2b followed by 1.
>
> Comments/suggestions/opinions?
>
> Thanks,
>
> Martin
--
---
Robert E. McGrath, Ph.D.
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
1205 West Clark
Urbana, Illinois 61801
(217)-333-6549
mcgrath@ncsa.uiuc.edu